I. Field of the Invention
The present invention relates generally to a device and non-surgical method for treating certain cardiac defects. More particularly, the present invention relates to a low profile occlusion device for non-surgical treatment of a patient having a Patent Foramen Ovale (PFO) and resulting paradoxical cerebral emboli. The device made in accordance with the invention is capable of automatically adjusting to a septal defect having eccentric openings and is particularly well suited for delivery through a catheter or the like to a remote location in a patient's heart or in analogous vessel or organ within a patient's body.
II. Description of the Related Art
A wide variety of intra cardiac devices are used in various medical procedures. Certain intravascular devices, such as catheters and guide wires, may be used to deliver fluids or other medical devices to a specific location within a patient's heart. For example, a catheter may be used to reach a selective coronary artery within the vascular system or the catheter and/or guidewire may be used to deliver a device to an interior chamber of the patient's heart. Complex devices may be delivered and used in treating specific abnormal conditions, such as devices used in removing vascular occlusions or devices used in treating septal defects and the like.
Balloon catheters and collapsible preformed polymeric devices similar to that disclosed by Landymore et al. in U.S. Pat. No. 4,836,204 and Linden et al. in U.S. Pat. No. 5,634,936 respectively have been used to occlude a septal defect. When using a balloon catheter similar to that disclosed in the '204 patent, an expandable balloon is carried on a distal end of the catheter. When the catheter is guided to the desired location, the balloon is filled with a fluid until it substantially fills the vessel and becomes lodged therein. Resins which will harden inside the balloon, such as an acrylonitrile, can be employed to permanently fix the size and shape of the balloon. The balloon can then be detached from the end of the catheter and left in place. The '936 device is expanded and hardened by a ternary system that modifies the pH and hydrophilicity of the device (see '936 patent, col. 6, ln 40-45). If these devices are not expanded completely they may not firmly lodge in the septal defect and may rotate and loosen from the septal wall, thereby releasing into the blood stream. Overfilling the '204 device is an equally undesirable occurrence which may lead to the rupture of the balloon and release of resins into the patient's bloodstream.
Mechanical embolization devices have been proposed in the past for occluding defects in a patient's intravascular system. The devices typically include a pair of spaced apart patches each having an internal collapsible frame (similar to the frame and outer membrane of an umbrella), wherein the opposing patch and frame are interconnected by a conjoint member. The patches are typically aligned and attached to a common axis of the conjoint member. The conjoint member may be a rigid or semi-rigid hub which minimizes the movement of the patches both laterally and fore and aft to thereby firmly retain the patches against the septal wall adjacent the defect. Patches that are attached to a common axis of the hub may become problematic when the septal defect to be occluded has eccentric openings. Since the patches are attached to a common rigid axis, at least one of the eccentric openings may not be completely covered by the respective patch. The rigid or semi-rigid hub prevents adjustment of the patches to compensate for the eccentric openings.
Representative examples of such mechanical devices are disclosed in King et al., U.S. Pat. No. 3,874,388 (the '388 patent), Das, U.S. Pat. No. 5,334,217 (the '217 patent), European application No. 0541,063 A2 (the '063 application), Sideris, U.S. Pat. No. 4,917,089 (the '089 patent), and Marks, U.S. Pat. No. 5,108,420 (the '420 patent). These devices are typically pre-loaded into an introducer or delivery catheter prior to the implantation procedure and are not commonly loaded by the physician during the medical procedure. During deployment of these devices, recapture into the delivery catheter is difficult if not impossible, thereby limiting the effectiveness of these devices.
Prior to implantation of these devices, the thickness of the septal wall near the defect and the approximate width of the defect must be determined in order that an appropriately sized device may be provided. A balloon catheter and a calibrated guidewire having radiopaque regions of known length, may be utilized by a physician during a preliminary fluoroscopic procedure to estimate the defect's size, shape and thickness of the septal wall near the defect. Although useful, the defects exact size and shape cannot be determined, thereby increasing the possibility of leakage around the occluding device. Hence, a device that inherently adjusts to the shape and thickness of the defect would be desirable.
Significantly, the size of the prior devices is inherently limited by the structure and form of the device. Also, when using occluding devices such as those disclosed in the '089, '388, '217, or '420 patents to occlude a septal defect, the pressure and therefore the chance of dislodgment of the device increases with an increase in size of the defect. Consequently, the prior devices require an oversized retention skirt positioned on each side of the defect. Oftentimes, the position of the septal defect dictates the size of the retention skirt. In a membranous type septal defect, it is difficult if not improbable to be able to effectively position the '388, '217, '089, or '420 device without at least partially closing off the aorta. Also, these disclosed devices tend to be rather expensive and time-consuming to manufacture.
Further, the shape of the prior devices (for example squares, triangles, pentagons, hexagons and octagons) require a larger surface contact area and have corners which may extend to the free wall of the atria. Each time the atria contracts (approximately 100,000 times per day) the comers extending to the atria walls are bent, creating structural fatigue fractures in approximately 30 percent of all cases. Furthermore, the previous devices require a French 14-16 introducing catheter, making it impossible to treat children affected with congenital defects with these devices. Hence, it would be advantageous to provide a reliable embolization device which is both easy to deploy through a 6-7 French catheter and which automatically adjusts to the shape and thickness of the defect. The present invention addresses these and other disadvantages of the prior art.